In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions is urged toward the rotating disk by a suspension. An air-bearing develops under slider and causes it to fly. The term “fly height” and air-bearing height will be used interchangeably herein. Fly heights are shrinking as the demand for increased areal density increases. A slider fly height of less than 10 nm is required for areal densities greater than 60 Gb/in2. To reach the 1 Tb/in2 mark, fly heights in the 2-3 nm range are needed. Fly heights this low place strict requirements on the allowable roughness of the disk surface.
Typically the last thin film layer which is vacuum deposited on the disk is a protective overcoat. Various carbon-based materials are currently in use for the overcoat such as diamond-like carbon, CHx and CNx, but many other materials are being explored. After the thin films have been deposited onto the disk a lubricant is applied to overcoat.
The manufacturing process for disks includes steps at various phases to reduce the roughness. One process commonly used is called “tape polishing.” After the lubricant has been applied onto the disk, a tape with an extremely fine abrasive bonded thereto is used to polish the surface of the disk. Although a tape has been traditionally used, various methods of polishing can be employed. The disk's suitability as a flying surface for the slider is typically tested after this abrasive polishing in what is called a “glide test.”
The requirements placed on the disk surface are so strict that subtle interactions between the thin films, the lubricant and the abrasive polishing can have a large effect on the yields of the manufacturing process.